One way of inducing temporary male infertility is to suppress the production of spermatozoa in the testis. So far, all drugs tested in this respect for human use were aiming at this effect.
In animal experiments, however, another way has been tried, namely using drugs inducing a temporary infertility by altering the functional properties of the spermatozoa without interferring with their production.
Studies of such drugs are rather easily carried out when using animals as test objects, viz. by letting medicated males copulate with new females each time. The resulting number of litters will then be an objective measure of the effectivity of the drugs and can be used for evaluating the effect of the drug in question.
One of the most extensively studies drugs of this kind is .alpha.-chlorohydrin, which has proved very effective in rats, but less effective or totally ineffective in other animal species. These findings raise the problem of species specificity of reproductive processes as well as of the drugs influencing the said processes.
Obviously, testing male fertility in human studies is difficult and, even when possible, proves time consuming and disclosing that a number of factors may influence the functional properties of the spermatozoa.
Thus, studying of these problems during the last 15 years makes me believe that functional parameters, such as the mobility pattern and survival of the spermatozoa under different conditions, their metabolism, their uptake and release of specific substances, and their resistance to various physical and chemical factors, could be deciding for the ability of the spermatozoa to fertilize the ova.